Patent GB-1474444-A (GB)
Title: Colour phase matching system for magnetic video tape recording
IPC: G11B27/028
Filed: 1974-08-22
Abstract: 1474444 Controlling video tape recorders ORROX CORP 22 Aug 1974 [22 Aug 1973] 36991/74 Heading G5R Proper colour burst phase matching of successive video recordings made on a tape by a magnetic tape recorder is ensured by coding each video recording on the tape to identify alternate frames to thereby provide a synthetic colour burst phase reference signal, comparing the colour burst phase of a video segment to be recorded with the synthetic phase reference signal, and, in dependence on the result of such comparison, controlling the tape speed and/or position to thereby correct the recording tape frame position relative to the colour burst phase of the video segment to be recorded when required to ensure proper colour burst phase matching. The invention is applicable to PAL and NTSC formats. In an editing apparatus for NTSC signals, a plant sync. source 20 gives a 3À58 MHz reference signal, with which the colour bursts of the output signals from playback VTR's (12), Fig. 1 (not shown), are in phase independent of the tape colour burst phase of a record VTR (14) and regardless of tape speed changes in the VTR's (12), and source 20 also gives a 30 Hz reference signal which synchronizes the VTR's with each other as well as forcing the playback VTR's (12) to be slaved to the record VTR (14). The 30 Hz signal also passes via a divider 22 to give a 15 Hz frame reference signal to a circuit 24 which computes the phase of the frame reference signal at the projected time of the start of recording on VTR (14) from one of VTR's (12). In response to a frame code signal, recorded on the tape of VTR (14) to permit alternate frames to be identified, a circuit 26 determines whether the frame number will be odd or even at said projected time of the start of recording. To make an insert into previous material on the tape on VTR (14), or to resume a previous edit session, a trial edit is made and the colour burst phase match-up is checked by means not shown; if the phases are properly matched the control 18 operates as below to ensure that all subsequent edits in that session will be colour phase matched, but if the phases are not properly matched it is necessary to operate a switch 32 to reverse the decision of comparator 28 whereafter control 18 will operate in the required way. Comparator 28 compares the outputs of circuits 24 and 26 to determine whether at the projected start of recording on VTR (14) the colour burst of the video signal to be recorded will properly match with that of the video signal already recorded on VTR (14); if the burst phases will be properly matched control 18 allows the normal editing synchronizing process to proceed to start recording on VTR (14) at the projected time, whereas if the colour burst phases would not properly match control 18 gives an output signal whereby during the synchronizing process the tape drive of VTR (14), and thus also those of the slaved VTR's (12), is slowed down so that the actual start of recording on VTR (14) is delayed from the projected start by the duration of one frame but occurs at the same frame code as it would have done without the slowdown and now has the colour burst phases properly matched at the edit point. Control 18 may alternatively operate, when necessary, to slow down or speed up the tape drives so that any odd number (for NTJC) of frames are "lost" or "gained" in time. The alternate frames may be identified by means of the least significant digit of the SMPTE time code on the cue track of VTR (14), or the alternate frame identification may be inserted within the video sync. or within the control track, or may be provided by a high frequency signal encoded in the audio track or by physically marking the tape of the record VTR (14).